1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming method, and a computer program product.
2. Description of the Related Art
In typical image forming apparatuses, a technology is commonly implemented in which a laser diode used as a light source emits laser light and the laser light is deflected by a polygon mirror so that a photosensitive element is main-scanned to be formed with a latent image. Particularly, in recent years, a technology has been known that makes use of a plurality of LDs, a laser diode array (LDS), or a vertical cavity surface emitting laser (VCSEL) for forming a latent image of a plurality of lines in a single scan.
For example, Japanese Patent Application Laid-open No. 2004-25828 discloses a technology in which, on the basis of a synchronization signal generated when a photoelectric conversion element (PD) detects the scanned laser light, a main-scanning synchronization signal (line data request signal) is generated with the purpose of determining an image data transfer timing to an image processing unit such as an application board that performs image processing, and thereby image data of a plurality of lines required to perform the writing operation in each scan is ontained.
In recent image forming apparatuses such as copying machines or printers in which the developer transferred onto a paper sheet gets fixed thereon by the application of heat, when images are printed on both sides of a paper sheet, the paper size before the application of heat is slightly different than the paper size after the application of heat, then the printed image on the front side and the printed image on the back side fall out of alignment. The reason for that is given below. After applying heat, the paper size undergoes slight shrinking as compared to the paper size before the application of heat. Thus, the printed image formed on the front side before the application of heat also undergoes shrinking. However, on top of that, another printed image is formed on the back side of the shrunken paper sheet thereby causing misalignment in the printed images.
In order to solve such a problem, a conventional technology is known in which magnification adjustment is done in the main-scanning direction as well as in the sub-scanning direction during the image processing performed by an image processing unit such as an application board. Alternatively, a conventional technology is known in which the magnification in the sub-scanning direction is adjusted by changing the rotating speed of the polygon mirror between both sides of a paper sheet and the magnification in the main-scanning direction is adjusted by performing data modulation or clock modulation using a write control unit. Still alternatively, a conventional technology is known in which the magnification in the sub-scanning direction is adjusted by the image processing performed by a write control unit without varying the rotating speed of the polygon mirror and the magnification in the main-scanning direction is adjusted by performing data modulation or clock modulation using the write control unit.
In such conventional technologies, particularly in image forming apparatuses in which images are reduced in size by means of thinning; all the data needs to be transferred sooner than normal from an image processing unit such as an application board. That requirement is met by increasing the number of line data request signals as requests for image data output to the image forming unit during a predetermined time period equivalent to a single scan.
However, due to various factors such as an increase in the print speed, an increase in the number of write lines during a single scan leading to an increase in the number of requests for the obtained image data during a predetermined time period, or a demand for slowing down the transfer rate of the image data obtained during a predetermined period time; the increased line data request signal output to the image forming unit overlaps into the subsequent predetermined time period thereby causing failure in the data transfer. That leads to the deterioration in the image quality.